To reduce fastener use or to militate against positional deviations, an interference fit is desirable for many components of machine assemblies. Typically, the interference fit is formed by joining a slightly oversized male component with a female component or by joining a slightly undersized female component with a male component. Particularly, the interference fit is desirable when joining components of driveshaft assemblies.
However, depending on the ultimate use of the assembled components, an interference fit can produce undesirable secondary effects. For example, the interference fit may cause component fretting. Fretting results from repeated vibrational or cyclical stressing of two mechanically associated components. With respect to driveshaft assemblies in particular, fretting may occur due to torsional stresses exerted between a shaft and a driveshaft end component such that slight movements between the shaft and the driveshaft end component result in fretting. Thus, the more contact between the two components involved in the interference fit, the more accurate the alignment between the two components must be if fretting is to be prevented.
Further, the undesirable debris produced by the repeated vibrational or cyclical stressing of an interference fit may result in unwanted noise during operation. Undesired noise may also be produced by torsional stresses exerted between metal components having the interference fit.
Also, use of an interference fit between components of driveshaft assemblies can increase production time as a result of the need to press the components together during manufacturing. Lastly, as the interference fit is typically between two metallic components, the components must be sized very accurately, further increasing a manufacturing cost of the driveshaft assembly.
The prior art generally discloses the concept of disposing a spacer between mechanically associated components to try to overcome some of the aforementioned issues. However, the spacers disclosed in the prior art are designed to perform different functions, than the spacer of the present invention. For example, U.S. Pat. No. 4,530,674 discloses a coupling shaft that includes a non-metallic bushing disposed between male and female members. The coupling shafts in this patent are slidably connected and the male members include crowned surfaces. However, in contrast to the embodiments of the present invention, the male and female members of the '674 patent are not rigidly coupled to one another. Thus, where a bushing is employed in the coupling shaft, the bushing is a load bearing bushing thus performing a different function than the spacers of the present invention.
Similarly, U.S. Pat. No. 4,357,137 discloses a shaft coupling that includes male and female members and a plastic insert, where the male member is not rigidly coupled to the female member and the plastic insert transmits the load from one member to the other.
As another example, European Patent Application Publication No. EP 0 588 468 A2 discloses a component for coupling a keyed shaft to a keyed sleeve. However, unlike the embodiments of the present invention, the keyed shaft is not rigidly coupled to the keyed sleeve. The component, which is preferably formed from a plastic, bears the transmitted load and also permits some misalignment of the keyed shaft and the keyed sleeve. The component may incidentally militate against fretting that may occur when the keyed shaft and the keyed sleeve are formed from a metal.
European Patent Application Publication No. EP 0 990 809 A1 discloses a system for coupling rotary shafts that includes a keyed shaft, a sleeve insert, and a keyed sleeve. The keyed shaft and the sleeve insert are slidingly disposed in the keyed sleeve and the sleeve insert is load bearing.
In addition, the spacers disclosed in the prior art are structurally different than the spacers of the present invention. For example, U.S. Patent Application Publication No. 2008/0286039 discloses a yoke bushing for reducing cyclic movement between a main shaft and a yoke. The yoke is rigidly coupled to the main shaft and the yoke bushing is disposed therebetween. The yoke bushing is a flexible structure that equalizes stress fields between the main shaft and the yoke. All embodiments of the '039 Application place particular emphasis on the upper and lower portions of the yoke bushing, and the middle portion either does not contact the main shaft or contains an elastomeric insert, unlike the present invention which relies on intimate contact between the central portion of the spacer and the shaft to form the interference fit.
As another example, the shaft and sleeve embodied in European Patent Application Publication No. EP 0 990 809 A1 may be splined and the sleeve insert may be a split insert. Whereas, the annular spacer embodied in the present invention have a hollow, generally tubular shaped body.
As seen by the above discussion, the spacers of the prior art are usually between components that are not rigidly coupled. Such spacers can be load bearing, functional components of the mechanical assemblies at issue.
Thus, it would be advantageous to develop a spacer for a driveshaft assembly that is easy to manufacture and/or install and will militate against fretting wear between rigidly coupled mechanically associated components, facilitate assembly, and militate against undesired operational noise of the driveshaft assembly.